1. Field of Invention
This invention relates generally to the field of microbial fuel cells and, more particularly, to miniaturized microbial fuel cells suitable for bioimplantation as well as to components and microfabrication techniques related thereto.
2. Description of the Prior Art
The use of biochemical activity of microorganisms to generate electricity has been studied by several groups of investigators. See, for example, the work of Kim et al (U.S. Pat. No. 5,976,719), Zeikus et al (U.S. Pat. Nos. 6,270,649 and 6,495,023) and references cited therein. Indeed, microbial electrochemistry and the generation of electrical power by means of a microbial fuel cell is sufficiently well developed to have become a teaching tool. For example, see H. P. Bennetto, “Electricity Generation by Microorganisms”, appearing in Biotechnology Education, Vol. 1, No. 4, pp. 163–168 (1990). Typical applications for microbial fuel cells have included the generation of electricity as a useful by-product from otherwise economically burdensome waste products, such as sewage sludge.
Other approaches to microbial electricity generation have included the use of isolated enzymes, typically immobilized on an electrode, rather than living microbes as the source of electromotive force. For example, see the work of Heller (U.S. Pat. Nos. 6,294,281 and 6,531,239), Liberatore et al (U.S. Pat. No. 6,500,571), Katz et al (J. Electroanaly. Chem., Vol. 479, pp. 64–68 (1999)), and references cited therein. Other approaches to fuel cell operation include the direct methanol fuel cell of Bostaph et al (U.S. Pat. No. 6,497,975) and the anaerobic oxidation of hydroxylic compounds in the presence of a quinone (Hertl et al, U.S. Pat. No. 4,578,323).
Concurrently with developments in microbial fuel cell technology, the need for miniature sources of electrical power has expanded due in part to advances in microdevices, MicroElectroMechanical Systems (MEMS) and implantable biomedical devices such as pacemakers, sensors, pain relief stimulators, among others. Implantable devices in particular call for a long-term power source, compatible with long-term residence in a human or animal biological system. Lithium batteries have been used for many years in high-power applications such as cardiac pacemakers, defribulators, among others. However, lithium battery power sources tend to be relatively bulky and expensive. Thus, various researchers have investigated biofuel cells to power implantable devices. See, for example, the non-microbial, glucose-powered fuel cell of Yao et al (U.S. Pat. No. 4,294,891), and the pacemaker power by a biofuel cell of Sturm et al (U.S. Pat. No. 3,941,135).
The miniature fuel cells operating on chemical fuels without the intervention of a microbe typically require replenishment or reactants and/or catalysts after a shorter interval than would be desirable for an implantable device. Conversely, the microbial fuel cells of the prior art are typically too bulky, chemically and/or biologically incompatible for use in conjunction with implantable devices. Thus, in view of the foregoing, a need exists in the art for an inexpensive, miniature, implantable power source capable of providing power to implantable or other MEMS devices for long periods of time.